There are a number of significant phosphate deposits from which is produced phosphate for chemical feed and fertilizers. These phosphate deposits can contain potentially economic quantities of uranium. For instance, phosphate rock is mined and processed in Florida (and other plants in the US) to produce a variety of high value agricultural products. The phosphate rock contains uranium in low quantities (for example, 100-200 ppm of uranium may be present in phosphate rock depending on the source of the phosphate rock). During the acid digestion stage of the wet-process phosphoric acid (WPA) process this uranium is solubilized into the phosphoric acid, which is further processed to manufacture the products of the plants.
Phosphoric acid producers have previously recovered uranium from WPA prior to production of fertilizer products using a variety of solvent extraction (SX) processes and these technologies are well understood in industry. Several plants operated over the years and one plant operated until the late 1990's. All plants were closed down due to high operating costs and the long term depressed uranium market.
With the recent revival of the uranium market there is renewed interest in the recovery of uranium from WPA. However, there is resistance to simply revert back to the historical processes for a number of reasons:
Historical high operating cost: The SX circuits operated in the past have had operating costs that were in the 3rd and 4th quartile of uranium producers, despite years of research and incremental operational improvements.
Operational difficulties: The SX circuits had numerous operational and maintainability issues that attributed to the high operating cost, but also led to downtime affecting production rates.
Decreasing ore quality: Over the past 20 years the quality of phosphate resources has been decreasing, i.e., a reduction in phosphate content and an increase in deleterious components. In particular the addition of metallic iron, which may be required for the processing of uranium, has become a more important issue due to increased iron levels in the ore, and subsequently in the WPA.
Waste management: The historical process produced a significant amount of radioactive solid waste that requires disposal. In the past, this waste has been co-disposed with the gypsum with limited regulatory issues; however, because of regulatory changes this co-disposal is no longer viable, and now the ability to economically dispose of any radioactive solid waste produced is uncertain. It can however, be safely assumed that the disposal of radioactive solid waste will be an expensive and difficult exercise.
Volatile uranium prices: The uranium price has risen dramatically in the past 2 years from historical lows to peak around US$135/lb. The long term predictions for the uranium price vary dramatically. This instability leads to a project operating in the 3rd or 4th quartile of production being very high risk, as the WPA uranium production plants have been in the past.
Thus, there is a need for a process for the extraction of uranium from wet-process phosphoric acid that will overcome at least some of these difficulties and provide a useful alternative to the industry.